This invention relates to a method for correcting the radial runout of a tire and rim wheel assembly. More specifically, the method allows to minimize the radial runout of tires and of the tire and rim assembly without dismounting the assembly from the vehicle or dismounting the tire from the rim. The method allows further to correct ride vibration problems associated with large tires and rims specifically designed for off-road or agricultural use.
The wheel assembly runout is due to a combination of the tire""s runout, the rim""s runout and the tractor""s hub runout. These three runouts increase the total assembly runout if they are in phase or they may decrease the total assembly runout if their phasing is optimized. Bouncing or vertical shaking oscillations the tractor""s driver experiences when running at speeds above 20 km/h on roads is directly related to the tire wheel assembly radial runout.
Large tires for tractors and the like vehicles may be mounted on large one or two piece rims. The rim is adapted to hold the tire. The rim has a 5xc2x0 bead seat, a pair of axially outer flanges, and a drop center portion to facilitate mounting the tire over the flange portions.
In case of one piece rims, the prior art methods to correct the tire wheel assembly vibration characteristics involve the steps of locating the maximum radial runout of the tire-rim assembly, the minimum radial runout of the rim, deflating the tire, breaking down the beads and rotating the tire to a distinct, precise location on the rim, remounting the tire rim assembly and reinflating the tire. This method of vibration reduction is commonly referred to as match mounting. The match mounting method is inherently time consuming, requires the tire beads to be detached from the rim, and after completing this procedure no positive result can be guaranteed. Furthermore the measurements only provide information on the tire-rim assembly and not on the tire itself, which information could help in choosing another rim wherein the tire would perform correctly.
In case of two piece rims, the radially outer portion is an annular ring. This annular ring further has a radially inner flange with a plurality of clearance holes to which the second portion of the rim is attached. The second portion of the rim is a disk which has a central opening which preferably is tapered, this central opening engages the drive axle of the vehicle to which it is attached. Radially outward of the central opening is a plurality of holes which can be aligned with the openings of the rim and bolted to the rim by means of threaded fasteners. These attachment holes in both the rim and the disk portion each have a clearance or relatively larger opening to accept the threaded fasteners. The dimensional tolerances permit the mounted tire and rim assembly to have their respective axis of rotation to be shifted relative to the common axis of the vehicle axle and wheel disk assembly. This ability to shift the relative position of the mounted tire and rim assembly relative to the disk portion can be positively beneficial in reducing tire and rim assembly vibration on tractors.
WO-A-97/39325 relates to a method for minimizing the radial runout of such two piece rims. The method can be summarized by the following steps:
locating the position of maximum radial runout and measuring the amount of maximum radial runout;
loosening the threaded fasteners;
moving the disk radially toward the location of the maximum radial runout a distance one-half the measured maximum runout amount, and then tightening the threaded fasteners thereby securely attaching the disk to the tire and outer rim of the assembly.
The present invention has as object to determine in the field the individual tire runout and the rim runout. A further object is to give indications on the contribution of the tire and rim assembly to the bouncing of the assembly. A still further object is to predict the match mounting for the tire on the rim and the remaining optimized assembly radial runout after match mounting.
The invention provides a method for minimizing the radial runout of a tire and rim assembly, as defined in the claims which are summarized as follows.
A method for minimizing the radial runout of a tire and rim assembly, has the steps of:
a) measuring the amount of radial runout along the radially outer portions of the tread lugs by rotating the tire rim assembly around its axis;
b) measuring the radial runout of the axially inner portions of the rim by rotating the tire rim assembly around its axis;
c) calculating the first and second harmonics of the rim;
d) subtracting point by point the first and second harmonic of the rim from the radial runout of the assembly;
e) analyzing the data obtained under step (d) as representing the runout of the tire alone;
f) discarding the tire if the data obtained under step (e) fall outside a given range.
g) discarding the rim if the data obtained under step (b) fall outside a given range.
In step (b), two axially inner portions of the rim facing both tire beads can be measured; and the average value determined and used in the calculation based on step (b).
Under step (d), the maximum of the first harmonic can be considered as representing the maximum runout of the tire; and the tire is marked at that location.
The first harmonic of the data obtained under step (b) can be used such that the minimum of the first harmonic is considered as representing the minimum runout of the rim; and wherein the rim can be marked at that location.
The markings on the tire and on the rim can be aligned so as to match-mount the assembly.
The data obtained under step (d) can be used to represent the curve of the runout of the tire alone and to determine the maximum runout of the tire, and the sum of the first and second harmonic of the rim can be considered to represent the curve of the radial runout of the rim alone and from that curve one can determine the minimum runout of the rim. By matching the obtained maximum runout of the tire with the minimum runout of the rim one can consider the result as representing the match mounted tire and rim assembly and can thus predictively calculate point by point the curve of the radial runout of the assembly. Alternatively, by matching the calculated minimum runout of the tire with the maximum runout of the rim one can consider the result as representing the match mounted tire and rim assembly.
The method enables one to select a different rim, make the measurements under step (b) and predictively calculate point by point the radial runout of the assembly without ever making the assembly.
The advantages of the invention are that its implementation is fast and easy. The farmer obtains within a short time an answer on the cause of the bouncing, an indication of what exactly must be done to at least partly remove such as well as what ride behavior can be expected after match mounting.
For ease of understanding this disclosure the following terms are used:
xe2x80x9cAspect Ratioxe2x80x9d means the ratio of the tire""s section height to its section width.
xe2x80x9cAxialxe2x80x9d and xe2x80x9caxiallyxe2x80x9d mean the lines or directions that are parallel to the axis of rotation of the tire.
xe2x80x9cBouncexe2x80x9d or xe2x80x9cHopxe2x80x9d means the vertical acceleration related to first Harmonic Radial Runout or Force Variation of each tire and rim assembly interacting with the other tire and rim assemblies of the vehicle.
xe2x80x9cCircumferentialxe2x80x9d means lines or directions extending along the perimeter of the surface of the annular tire parallel to the equatorial plane EP and perpendicular to the axial direction.
xe2x80x9cDesign Rimxe2x80x9d means a rim having a specified configuration and width. For the purposes of this specification, the design rim and design rim width are as specified by the industry standards in effect in the location in which the tire is made. For example, in the United States, the design rims are as specified by the Tire and Rim Association. In Europe, the rims are as specified in the European Tyre and Rim Technical Organizationxe2x80x94Standards Manual and the term design rim means the same as the standard measurement rims. In Japan, the standard organization is The Japan Automobile Tire Manufacturer""s Association.
xe2x80x9cEquatorial Plane (EP)xe2x80x9d means the plane perpendicular to the tire""s axis of rotation and passing through the center of its tread.
xe2x80x9cFootprintxe2x80x9d means the contact patch or area of contact of the tire tread with a flat surface at zero speed and under normal load and pressure.
xe2x80x9cInnerxe2x80x9d means toward the inside of the tire and xe2x80x9couterxe2x80x9d means toward its exterior.
xe2x80x9cLateral Edgexe2x80x9d means the axially outermost edge of the tread as defined by a plane parallel to the equatorial plane and intersecting the outer ends of the axially outermost traction lugs at the radial height of the inner tread surface.
xe2x80x9cLeadingxe2x80x9d refers to a portion or part of the tread that contacts the ground first, with respect to a series of such parts or portions, during rotation of the tire in the direction of travel.
xe2x80x9cLopexe2x80x9d means once per revolution fore and aft acceleration/deceleration related to first harmonic radial runout or force variation of tire and rim assembly.
xe2x80x9cNet-to-gross Ratioxe2x80x9d means the ratio of the surface area of the normally loaded and normally inflated tire tread rubber that makes contact with a hard flat surface, divided by the area of the tread, including noncontacting portions such as grooves as measured around the entire circumference of the tire.
xe2x80x9cNormal Inflation Pressurexe2x80x9d means the specific design inflation pressure assigned by the appropriate standards organization for the service condition for the tire.
xe2x80x9cNormal Loadxe2x80x9d means the load assigned by the appropriate standards organization for the service condition for the tire when inflated to the normal inflation pressure.
xe2x80x9cRadialxe2x80x9d and xe2x80x9cradiallyxe2x80x9d mean directions radially toward or away from the axis of rotation of the tire.
xe2x80x9cShakexe2x80x9d means higher frequency lug induced vibration felt in cab or steering wheel or seen in movement of the exhaust stack (no particular acceleration).
xe2x80x9cShudderxe2x80x9d means a lug induced vibration at low frequency, resulting in a vertical acceleration felt through the floor of the cab.
xe2x80x9cTrailingxe2x80x9d refers to a portion or part of the tread that contacts the ground last, with respect to a series of such parts or portions during rotation of the tire in the preferred direction of travel.
xe2x80x9cTrampxe2x80x9d means side-to-side motion, or lateral acceleration, induced by first harmonic radial runout or force variation of each tire and rim assembly interacting with each other.
xe2x80x9cTread Arc Widthxe2x80x9d (TAW) means the width of an arc having its center located on the equatorial plane (EP) and which substantially coincides with the radially outermost surfaces of the various traction elements (lugs, blocks, buttons, ribs, etc.) across the lateral or axial width of the tread portions of a tire when the tire is mounted upon its designated rim and inflated to its specified inflation pressure but not subject to any load.
xe2x80x9cUnit Tread Pressurexe2x80x9d means the radial load borne per unit area (square centimeter or square inch) of the tread surface when that area is in the footprint of the normally inflated and normally loaded tire.
xe2x80x9cVibration Ratingsxe2x80x9d mean the subjective ride terminology wherein xe2x80x9cslightxe2x80x9d means rely noticeable; xe2x80x9cmoderatexe2x80x9d means noticeable but not objectionable; xe2x80x9cseverexe2x80x9d means objectionable.